The present invention relates generally to imager and memory wafers, and more particularly to through-wafer interconnects and blind vias for imager and memory devices.

As depicted in FIG. 1, a conventional bond pad structure 100 is built on a silicon substrate 110 covered by an oxide layer 120. The bond pad 130 is embedded within a passivation layer 140. A conductive gold wire (160) ball (150) bond is formed and attached on a central upper surface of the bond pad 130.

A disadvantage of direct bond pad connection on the top side of the die, as depicted in FIG. 1, includes the fact that they sometimes require a wire bond 160 to be electrically connected to a lead frame or other structure for final die packaging. Another method that involves flip chip packaging at the wafer level involves a re-distribution layer (RDL) that allows the bond pad pitch to be routed to a more useable pitch in order to attach a solder ball directly on the top side of the die. Both of these packaging approaches involve contacting the bond pads on the top side of the die. As a result, this limits the ability to stack memory and imager devices. Furthermore, the ability to attach the cover glass on imager wafers at the wafer level is limited due to the requirement to make contact to the bond pad on the top side of the wafer. Accordingly, it is desirable to develop a through-wafer interconnect to eliminate the need for wire bonding, to increase the volumetric circuit device density, to minimize the size of the die's packaging, to make memory devices stackable and to enable wafer level packaging (WLP) methods for imager wafers.

The present invention addresses the shortcomings described above and provides in disclosed exemplary embodiments a through-wafer interconnect for imager, memory and other integrated circuit applications, thereby eliminating the need for wire bonding, making devices incorporating such interconnects stackable to allow increased volumetric density and device functionality and enabling WLP for imager devices. Further, a smaller and more reliable die package is achieved and circuit parasitics (e.g., L and R) are reduced due to the reduced signal path lengths.

In the following detailed description, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those of ordinary skill in the art to make and use the invention, and it is to be understood that structural, logical or procedural changes may be made to the specific embodiments disclosed without departing from the spirit and scope of the present invention.

FIG. 2 depicts a portion of a semiconductor wafer 200 at a stage of a process for manufacturing a through-wafer interconnect for an integrated circuit device. A bond pad 240 is depicted as being formed over a silicon (Si) substrate 230 and within a passivation layer 220 or layers. Beneath the passivation layer 220 is a borophosphosilicate glass (BPSG) layer 225. The bond pad 240 is depicted as being a monolithic structure, however, the bond pad 240 may take other forms including a multiple tiered structure. When the wafer 200 is an imager wafer, this portion of the process may be performed either prior to or after a color filter array (CFA) 720 and microlenses 710 (depicted in dotted lines) have been formed on the top surface of the wafer 200. One advantage to forming the interconnect prior to forming the CFA 720 and lenses 710 is that the CFA and lenses may be somewhat delicate and sensitive to heat; thus, forming the interconnect prior to their formation may result in less risk to damaging the array.

FIG. 3 depicts a hole, or via, 300 formed in a center of the bond pad 240 from the passivation layer 220 down through the substrate 230. The initial opening to create the hole 300 is formed by sequences of patterning and etching (either wet or dry) through the dielectric and metal layers. For instance, a dry etch may be performed to remove the top portion of passivation layer 220. A dry etch may be performed through the metal 240. A dry etch may be performed through the BPSG layer 225. A wet etch may be performed to form the initial hole 300 in the bulk silicon and to form an initial dimple in the Si 230. A laser drill process or deep silicon, dry etch process may then be conducted on the Si substrate 230, followed by a wet clean process. Also depicted is the application of a dielectric 310 to line the walls of the hole 300 and to electrically insulate the subsequent conductive materials in the via from shorting to the bulk silicon substrate. The dielectric also covers the top of the bond pad 240 and the upper passivation layer 220. The dielectric 310 may be low silane oxide (LSO) or any known method to deposit dielectric films using ALD, CVD, PECVD or other means commonly used in the art.

FIG. 4 depicts the interconnect structure with the dielectric 310 removed from the passivation layer 220 and the bond pad 240 by a spacer etch process (e.g., chemical mechanical polishing (CMP) or a dry vertical oxide etch). The dielectric 310 remains as a liner of the walls of the hole 300.

FIG. 5 depicts a plating layer 410 of nickel on a seed material such as titanium nitride (TiN) or tungsten (W), or copper (Cu) on tantalum (Ta), or copper (Cu) on tungsten (W), or other conductive materials and other combinations of these materials, deposited on top of the dielectric 310 on the sidewalls of the via 300 and on top of a portion of the bond pad 240. The seed material or materials are removed from the top passivation surface by CMP or photo/etch processing. This removal process does not remove the material in the via or on the bond pad.

FIG. 6 depicts the hole 300 as being filled with solder 510 utilizing plating or molten solder. It should be noted that other conductive materials (e.g., copper, nickel, conductive polymers, etc.) may be used to fill the hole 300 and/or conductive materials may also be plated to fill the hole. (e.g., nickel, copper, etc.). A dielectric layer 610 is then applied to the lower surface of the wafer 200.

As depicted in FIG. 7, a CMP process may then be performed on the top surface 740 and the bottom surface 750. Another variation of the process is to use a wet etch rather then CMP to etch away the protruding solder 510 or nickel plating 800 (FIG. 8). It should be noted that the CMP process may not be necessary for memory device applications as the final surface topography may not be critical. For an imager wafer, the CFA 720 and lenses 710 are then formed on top of the upper flat surface 740. Performing a planarization process after the solder 510 fill operation helps to provide a smooth surface in which to apply the CFA and microlens material. The smooth wafer surface prevents streaking and other imperfections which can affect the optical performance of the CFA and microlens structures.

In accordance with an exemplary embodiment of the invention, the via 510 electrically connects bond pad 240 with the top surface 740 of the wafer and the bottom surface 750 of the wafer resulting in a much more efficient package that is stackable for memory devices and that lends itself to wafer level packaging for imager devices.

FIG. 8 depicts another exemplary embodiment in which the nickel plating 800 is flush with the passivation layer 220. In this embodiment, the top metal layer of the bond pad 240 is plated with nickel. In this manner, when the solder 510 filling the hole 300 is planarized by CMP, the nickel remains at the top-most portion of the through-wafer interconnect.

Turning to FIG. 9, an initial step in another exemplary process for forming a through-wafer interconnect with a blind via is depicted. An initial step in this exemplary process is to form a blind via that recesses only partially through a semiconductor substrate. A simplified illustration of a completed wafer is depicted as containing a silicon substrate 900 and a bond pad 920 provided near an upper surface which is surrounded by a passivation layer 910. The passivation layer 910 is located above an insulation layer, such as BPSG layer 930. As depicted in FIG. 10, the passivation layer is removed from an area over a portion of bond pad 920, by a dry etch process up to the bond pad 920 leaving an opening 1000 in the passivation layer.

As depicted in FIG. 11, a wet or dry metal etch is performed through the bond pad 920 down to surface 1100 of the BPSG layer 930. FIG. 12 depicts a nickel plating 1200 formed on the bond pad 920. An oxide etch is performed on the lower passivation layer and down to the top layer 1300 of the silicon substrate 900, as depicted in FIG. 13. FIG. 14 depicts the optional application of a polyimide coat 1400 to planarize and protect the frontside of the wafer from residual metals on the vertical surfaces of the wafer topography. These residual metals are formed when material is not sufficiently removed in previous CMP or wet or dry etch processing.

As depicted in FIG. 15, a resist coat 1500 is applied for performing a deep silicon etch. The results of the etch are depicted in FIG. 16 in which a via 1600 approximately 150-300 micrometers deep has been etched. The deep silicon etch resist coat 1500 is then stripped, as depicted in FIG. 17. FIG. 18 depicts the deposition of a dielectric material 1800 on the via 1600 sidewalls and other surfaces. The dielectric 1800 serves as an electrical insulation layer for the sidewalls. In FIG. 19, results of a spacer dry etch are depicted as having removed the dielectric from the surface 1400, but maintaining the dielectric 1800 on the via sidewalls.

Turning to FIG. 20, a seed layer of conductive material is formed on the dielectric and on the metal bond pads through processes known in the art such as e.g., CVD, PECVD, PVD. In FIG. 21, the seed layer is covered with photoresist 2150 to protect the surface from subsequent plating steps. Electroless or electrolytic nickel plating 2000 is depicted on the sidewalls 2010 of the via 1600 and also on the top portion of the bond pad 920. In the optional flow of using polyimide 1400, the polyimide 1400 may be stripped from the surface of the passivation layer 910 (FIG. 21). The via 1600 is filled with conductive material such as solder 2200 utilizing plating or molten solder as depicted in FIG. 22. FIG. 23 depicts a thinned wafer 2300 having been processed by backgrind, CMP, wet etch, dry etch, or any other thinning method known in the art.

FIG. 24 depicts an optional tetramethylammonium hydroxide (TMAH) silicon etch that exposed the dielectric 2410 on the bottom side of the via and causes the via insulation and via fill material to slightly protrude out from the backside surface. Regardless of whether the TMAH etch is performed, a dielectric deposition is applied to passivate the backside 2500 of the wafer, as illustrated in FIG. 25. With the via protruding in the manner described, CMP or a wet etch may be performed across the entire backside of the wafer in order to remove the insulating material covering the solder while maintaining a passivation layer over bulk silicon regions of the backside of the wafer.

As an alternate embodiment to CMP exposure of the solder on the backside of the wafer, turning to FIG. 26, a resist 2600 is applied to the backside of the wafer and in FIG. 27, the lower level of passivation is removed by applying a photo pattern and performing a wet oxide etch or dry spacer etch to expose the lower layer of solder 2700. The resist is stripped and a solder ball 2800 may be attached to the bottom of the via 1600, as depicted in FIG. 28. Alternatively, a solder ball 2800 could be attached to the top of the via 1600, or a solder ball 2800 could be attached to both the top and the bottom, or not attached at all.

As depicted in FIG. 28, a through-wafer interconnect 2830 is formed in which the interconnect 2830 extends from a topside surface 2810 of the wafer where it is electrically connected to a bond pad 920, to a bottomside surface 2820 of the wafer and in which a solder ball 2800 is attached and electrically connected to the bottomside surface of the interconnect 2830. As a result, the interconnect 2830 is actually part of the structure of the device or circuit included within the wafer and is more reliable, due to shorter connections and fewer parts, enabling a subsequent packaging size of the die to be greatly reduced and allowing die to be stacked with no wire bonding.

Turning to FIGS. 29-35, a second exemplary process for forming a blind via is depicted. The beginning of the second exemplary process is identical to the portions of the first exemplary process depicted above in connection with FIGS. 9-22 The process continues at FIG. 29, as described below.

FIG. 29 depicts a carrier 3500 bonded to the upper layer of the wafer with a carrier bonding adhesive 3520 and the wafer is thinned to surface 3510 though any thinning process known in the art. The carrier material could be a substrate such as silicon, glass, silicon nitride, aluminum nitride, or any other material suitable for use as a carrier substrate. The adhesive can be photoresist, photo-definable epoxy, an adhesive tape medium, UV releasable tape, etc. A TMAH silicon etch may be optionally performed to expose the via 3610 at the bottom of the via and cause it to slightly protrude from the surface, as depicted in FIG. 30.

FIG. 31 depicts a dielectric deposition 3700 to passivate the backside of the wafer and FIG. 32 depicts a resist and pattern 3810 applied to the backside of the wafer to prepare for an etch process on the backside. A wet passivation etch or dry spacer etch is performed to remove the backside passivation 3700 from the solder via 3900, as depicted at FIG. 33. This may also be accomplished with a light CMP or grind operation which leaves passivation material over the bulk silicon while allowing the solder to be exposed on the backside of the filled via. FIG. 34 depicts the removal of the resist 3810 and the application of solder ball 4010. FIG. 35 depicts removal of the carrier 3500.

Here again, a through-wafer interconnect 4100 is formed in which the interconnect 4100 extends from a topside surface 4110 of the wafer, where it is electrically connected to a bond pad 920, to a bottomside surface 4120 of the wafer and in which a solder ball 4010 is attached and electrically connected to the interconnect 4100. The interconnect is part of the structure of the device or circuit included within a die and is more reliable, due to fewer connections and external parts, enabling a subsequent packaging size of a die to be greatly reduced.

In accordance with exemplary embodiments of the invention, packaging solutions are described which eliminate wire bonding to bond pads. As a result, die performance and reliability are enhanced. Furthermore, these processes result in much smaller die packages which may be stacked and which lend themselves to WLP. Packaging costs are also significantly reduced as a result.

While the invention has been described in detail in connection with preferred embodiments known at the time, it should be readily understood that the invention is not limited to the disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. For example, although the processes are described in a specific order, some of the process steps may be performed in an order different than that described above. Further, while the processes are described in connection with imager and memory wafers, the invention is not limited to such applications. The invention may be practiced with other types of wafers as well as any device that would benefit from such a through-wafer interconnect. Accordingly, the invention is not limited by the foregoing description or drawings, but is only limited by the scope of the appended claims.